1. Field of the Invention
The present invention relates to a high-performance large aperture ratio telephoto lens system with the focal length about 200 mm to 300 mm.
2. Description of the Prior Art
For known telephoto lens systems with the focal length about 200 mm to 300 mm, the F number is about F4 in general. Even in case of bright lens systems, the F number is about F2.8 at the best. However, one of recent tendencies of interchangeable lenses for cameras of 35 mm format is to make the aperture ratio larger and a still brighter telephoto lens system is now being waited for. When, however, it is attempted to design a telephoto lens system with a large aperture ratio, it is difficult to favourably correct chromatic aberration to be caused by the secondary spectrum and to make both of spherical aberration and Petzval's sum small at the same time. Moreover, the lens system becomes large and long. Therefore, as telephoto lens system of F2 class, there is only one known telephoto lens system which is disclosed in Japanese published unexamined patent application No. 134425/78. However, the abovementioned telephoto lens system has a large telephoto ratio, i.e., about 1.23.